System for improving flexibility of riser supports in stationary production units and installation method

ABSTRACT

The present invention addresses to a system consisting of one or more pipes of low flexural rigidity (upper and intermediate extension pipes), connected to a thicker pipe section (lower extension pipe) by means of a varied cross-section pipe (conical profile) and further an adapter shaped like a helmet of a bend stiffener of a flexible riser, to enable, without operational losses, the use of rigid risers in Stationary Production Units (SPUs) initially designed to receive only flexible risers, therefore not having specific supports for rigid risers. The low flexural rigidity of the pipe is achieved through the correct selection of specific materials, preferably by using a titanium alloy that has a low modulus of elasticity and a high yield strength compared to steel.

FIELD OF THE INVENTION

The present invention addresses to a system consisting of one or more pipes of low flexural rigidity, applied in Stationary Production Units (SPUs), with the primary function of supporting rigid risers in an interface initially designed to receive only flexible risers.

DESCRIPTION OF THE STATE OF THE ART

The connection of rigid risers, also called rigid pipes, on anchored platforms is normally carried out by means of supports of the conical receptacle type (US6835025B1). In this support, the top accessory of the riser (flexible joint/stress joint) has an external profile in the shape of a truncated cone that is seated on the receptacle. The support of risers with receptacles is characterized by the transmission of tensile loads and bending moment to the SPU in a concentrated region, that is, the stresses are transmitted to the platform structure by a single support. In the support of flexible risers, also called flexible pipes, the oil industry has used support systems of the I-tube type with Bell Mouth (US005947642A). This support consists of two vertical guide tubes, one positioned at the height of the upper deck, and another in the lower region of the vessel hull, through which the flexible pipe passes. The lower I-tube has an angular deviation in relation to the vertical, and at its end the bell mouth is positioned, where the locking of the adapter helmet of the flexible bend stiffener is performed. In this configuration, the bending moment is transmitted to the vessel through the lower I-tube by the bend stiffener, while the tension is transmitted through the upper I-tube through the Hang-off. In the hypothesis of fixing rigid steel pipes in this support, it would imply several problems, such as: plastic deformation of the top tubes, local buckling due to localized compression of the tube against the helmet wall, etc. There are further support systems known as multifunctional bell mouths (MFBM), which were developed to receive rigid and flexible pipes. The MFBM resembles the I-tube/bell-mouth system. In the MFBM, the lower I-tube and the bell mouth are a single component and the entire lower support has the top angle inclination. In this type of support, the rigid pipe is completely supported by the MFBM in the lower region, while the flexible pipe continues with load separation. During the implementation of an offshore oil production development design, it is necessary to select the type of support system that will be installed in the SPU; accordingly, the support system of a unit is selected according to the subsea layout of the design. This procedure is natural, but brings little flexibility for future changes. With the appearance of the technical problem related to the occurrence of the phenomenon of CO₂ stress corrosion, intensified by the flooding of the annulus in flexible pipes, the oil operators had to evaluate the replacement of several flexible risers considered critical by rigid pipes. These flexible risers are found operating in units that have I-tubes and/or MFBM. In this scenario, the need arose to develop a riser top system that enables the connection of rigid pipes on supports that are prepared to operate with flexible risers.

Although the MFBM design allows for both rigid and flexible pipes, once a flexible riser is initially installed, there is no possibility of installing a rigid riser in its place. Considering this, the attempt to obtain flexibility occurred through the re-design (reworking) of the MFBM. Accordingly, in designs that used MFBM, there was a restriction on the application of rigid pipes in the conventional way before the invention.

The first approach developed to enable the connection of rigid risers in I-tubes considers the use of a hybrid riser, consisting of a section of flexible pipe (known as a “jumper”) mounted on the upper end of a rigid riser. All the support of the riser is done in the flexible pipe section, using typical accessories for this pipe. The use of this type of configuration brings several points of attention to the design. CO₂ stress corrosion remains a risk for the riser assembly. The feasibility study of the hybrid configuration suggests the prediction of two jumper changes over the life of the design, generating negative impacts both in oil production and in implementation and maintenance costs. The procedure currently envisaged for transferring the riser to the platform may restrict the number of support vessels to carry out the operation, or increase the number of vessels.

Document BR112018015179-3 A2 discloses a device for coupling a riser to a floating structure. The document, despite describing a device for coupling a riser having components such as a flexible joint, flanges and adapters, differs from the present invention by not presenting the same solution of the present invention, regarding the use of rigid risers in SPUs initially designed to receive flexible risers only.

Document US20180155994A1, despite disclosing a method of supporting rigid risers, mentioning the use of a rigid jumper (which may be made from titanium) that transports the fluids, contains the fluid pressure and accommodates angular deflections of the riser, and therefore differs of the present invention mainly because it does not show the use of rigid risers in a SPUs previously structured to receive only flexible risers.

Document BRPI0009911-2 B1 also does not have the adaptation for the installation of rigid pipes in a SPUs considering structured for flexible risers.

The present invention addresses to a system and method consisting of one or more pipes of low flexural rigidity with features related to diameter and thickness different from each other and which provide advantages over what is disclosed by documents of the state of the art, as they enable apply rigid pipes in systems designed to receive flexible risers only.

BRIEF DESCRIPTION OF THE INVENTION

The present invention addresses to a system consisting of one or more tubes of low flexural rigidity, the upper extension pipes and intermediate extension pipes, connected to a tube section of greater external diameter and thickness (lower extension pipe) by means of a varied cross-section (conical profile) and further an adapter with an external shape of helmet adapter of a bend stiffener of a flexible pipe, to enable, without operational losses, the use of rigid risers in Stationary Production Units (SPUs) initially conceived to receive only flexible risers, therefore not having specific supports for rigid risers. The selection of the material is based on the reduction of the flexural rigidity of the tubes and, mainly, on the increase of the mechanical strength. For application in pre-salt fields located in the Santos basin on the Brazilian shore, the use of a titanium alloy is being considered, because it has a low modulus of elasticity, much lower when compared to that of common steel, and a higher yield strength, also compared to ordinary steel. However, the invention is not restricted to the use of this material.

OBJECTIVES

The present invention aims at enabling the connection of rigid pipes on supports that are prepared to operate with flexible risers.

The present invention allows a life in service where the tensile and bending moment loads exerted on the supports are decoupled (separated).

The present invention aims, by proposing a selected material, at being immune to CO₂ stress corrosion and avoiding the same problem that occurred in the annulus of flexible risers.

The present invention aims at preventing the locking mechanism from being an integral part of the TTR.

The present invention aims at providing more flexibility in future changes after the implementation of an offshore oil production development design.

Another objective of the present invention is to simplify and reduce operating time for installing the riser or rigid pipe.

The present invention also has the objective of avoiding the contingency for the exchange of the top flexible jumper.

These and other objectives, such as flexible riser support, are achieved by the object proposed by the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be described in more detail below, with reference to the attached figures which, in a schematic way and not limiting the inventive scope, represent examples of the same. In the drawings, there are:

FIG. 1 illustrates the state-of-the-art rigid riser receptacle;

FIG. 2 illustrates the parts that make up the stresses in the state-of-the-art flexible riser support system;

FIG. 3 illustrates the Multifunctional Bell Mouth (MFBM) Support of the state of the art;

FIG. 4 illustrates the components of the system of the present invention;

FIG. 5 illustrates the embodiment of the present invention;

FIG. 6 illustrates the attachment of the adapter helmet.

DETAILED DESCRIPTION OF THE INVENTION

Preliminarily, it should be emphasized that the description that follows will be based on the preferred embodiments of the invention. As will be apparent to anyone skilled in the art, however, the invention is not limited to these particular embodiments, but rather to the scope of the claims.

The present invention, as shown in FIG. 4 , addresses to a top rigid riser with low flexural rigidity, an upper extension pipe (1) and an intermediate extension pipe (2) for the installation in an interface system of flexible risers connected to a thicker tube section of the lower extension pipe (3), by means of a varied cross-section pipe (4) with a conical profile and further an adapter with an adapter helmet shape (5) of a flexible pipe, to enable, without operational losses, the use of rigid risers in Stationary Production Units (SPUs) initially designed to receive only flexible risers, therefore not having specific supports for rigid risers.

FIG. 1 illustrates the state-of-the-art receptacle with rigid riser, highlighting the use of a flexible joint (10). FIG. 2 illustrates the two parts, one upper and one lower, which make up the segmented stresses respectively in tension (upper part) and bending moment (lower part) in the support system of flexible risers of the state of the art. There should be highlighted in this arrangement the use of a bend stiffener (17).

Before the pull in operation, transferring the tube to the platform, the adapter helmet (5) will be attached to the top of the tube by means of a collar containing fusible cables (8), as shown in FIG. 6 . During the pull in operation, the set of system tubes is pulled by the platform winch cable (12), passing inside the lower I-tube (13) and bell mouth (7) (or MFBM), illustrated in FIG. 3 . The adapter helmet (5) will enter the bell mouth (7), where it will be locked with its weight supported by Dogs (14) exactly as in a pull in of flexible pipes. The set of pipes (1, 2 and 3) continues to slide inside the adapter helmet (5) and (conventional/Multifunctional) bell mouth (7) until its top end reaches the upper I-tube (15), see FIG. 5 . When this occurs, a support (9) (hang-off) is mounted around the top flange (11) for fixing the tube (16) to the support (9) (hang-off), which surrounds the connector of riser (18) (end-fitting). This support (9) is similar to the support system of a flexible pipe.

During the service life of the riser, the lower extension pipe (3) will work inside the Bell Mouth (7) and the lower I-tube (13). Its function is to allow a smooth curvature through the transition of flexural rigidity. In this way, the upper extension pipe (1) and the intermediate extension pipe (2), preferably made of titanium and located just above the conical section of this section, support mainly an axial load. In summary, the low flexural rigidity promoted by the selection of materials and the external diameter transition profile of the extension pipes (1, 2 and 3) of the proposed configuration allow a transfer operation from rigid pipes to the SPU similar to the transfer of a flexible riser, in support for the latter. In addition, the present solution allows a lifetime in service where the tensile and bending moment loads exerted on the upper I-tube (13) and lower I-tube (15) are uncoupled. We can mention as additional advantages the technology able to receive the flexible joint (10) and/or a stress joint (not shown), the selection of materials that allows the use of material immune to CO₂ stress corrosion and the installation procedure similar to the ones used for conventional flexible pipes.

In this way, the present invention, given its embodiment, is available to be applied in Stationary Production Units (SPUs), with the primary function of supporting rigid risers in an interface initially designed to receive only flexible risers and have the following components:

-   upper extension pipe (1); -   intermediate pipe extension (2); -   lower extension pipe (3); -   varied cross-section pipe (4); -   adapter helmet (5); -   upper I-tube (15); -   lower I-tube (13); -   bell mouth (7); -   pipe interconnection fittings, flanges (6).

The system presents a very simple interconnection. The section of upper extension pipe (1) is the pipe section positioned at the upper end of the system. This pipe has a flange at the top that will be used to connect the platform piping, and a lower flange that will be connected to the intermediate extension pipe (2). The profile of these tubes is very similar and therefore they were not differentiated in FIG. 4 . The number of intermediate extension pipes (2) depends on the length between the upper I-tube (15) and the lower I-tube (13), in addition to limitations in length that are characteristic of the manufacturing process adopted to obtain the pipes (1) and (2). The lower end of the intermediate extension pipe (2) is connected to the lower extension pipe (3), which is the component responsible for promoting a smooth curvature of the tube inside the adapter helmet (5). The extension pipes (1), (2) and (3) are connected by means of flanges (6) of the compact type, or through circumferential welds, as illustrated in FIGS. 4 and 5 . The lower end of the lower extension pipe (3) is connected to a varied cross-section pipe (4), or to a stress joint, or to a flexible joint (10), as it occurs for specific designs.

The sequence for installing the rigid riser to the SPU, considering the new elements brought by the invention, must be:

-   Fixing the adapter helmet (5) to the upper extension pipe (1) by     means of a collar containing fusible cables (8); -   Starting the pull in procedure of the set of extension pipes (1, 2     and 3), already coupled together by means of flanges or welds, by     the platform winch cable passing inside the lower I-tube (13) and     through the bell mouth (7); -   Locking the adapter helmet (5), whose weight will be supported by     Dogs (14); -   Continuing to slide the set of extension pipes (1, 2 and 3) inside     the adapter helmet (5) and through the bell mouth (or     multifunctional bell mouth) (7) until its top end reaches the upper     I-tube (15), wherein, in this moment, the lower extension pipe (3)     due to its larger diameter locks onto the adapter helmet (5); -   Assembling a support (9) around the flange of the upper extension     pipe (1), and connecting the same to the vessel piping through a top     flange (11).

The proposed method is not restricted to the above embodiment, and may have small procedural variations according to the accessory elements. 

1. A system for flexibilization of riser support in stationary units, comprising an upper I-tube (15), a lower I-tube (13), a bell mouth (7), an adapter helmet (5), and characterized in that it comprises an upper extension pipe (1), an intermediate extension pipe (2), a lower extension pipe (3) and a varied cross-section pipe (4).
 2. The system according to claim 1, characterized in that the upper extension pipe (1) is positioned at the upper end of the system and has a lower flange that connects to the section of intermediate extension pipe (2).
 3. The system according to claim 2, characterized in that the number and length of sections of the intermediate extension pipe (2) depend on the distance between the upper I-tube (15) and the lower I-tube (13).
 4. The system according to claim 1, characterized in that the lower end of the intermediate extension pipe (2) connects to the section of lower extension pipe (3).
 5. The system according to claim 1, characterized in that the section of the lower extension pipe (3) promotes a curvature (flexion) inside the adapter helmet (5).
 6. The system according to claim 1, characterized in that the extension pipes (1), (2) and (3) are connected to each other by means of compact type flanges (6), or circumferential welds.
 7. The system according to claim 1, characterized in that the lower end of the lower extension pipe (3) is connected to a stress joint or flexible joint (10), replacing the varied cross-section pipe (4).
 8. An installation method of the system for flexibilization of risers according to the inventive concept presented in claim 1, characterized in that there are the following steps: Fixing the adapter (5) to the top tube (1) by means of a collar containing fusible cables (8); Starting the pull in procedure of the set of extension pipes (1, 2 and 3) by the platform winch cable passing inside the lower I-tube (13) and through the bell mouth (7); Locking the adapter helmet (5) whose weight will be supported by Dogs (14); Continuing to slide the set of extension pipes (1, 2 and 3) inside the adapter helmet (5) and bell mouth (or multifunctional bell mouth) (7) until its top end reaches the upper I-tube (15); Assembling a support (9) around the flange of the upper extension pipe (1), connecting it to the vessel piping through a top flange (11).
 9. The system according to claim 3, characterized in that the lower end of the intermediate extension pipe (2) connects to the section of lower extension pipe (3).
 10. The system according to claim 4, characterized in that the section of the lower extension pipe (3) promotes a curvature (flexion) inside the adapter helmet (5). 